Method of retarding the cooling of molten metal

Abstract

The cooling of molten metal, such as metal continuously cast into an ingot mold, is retarded by establishing on the upper surface of the metal in the mold, a layer of cryogenic liquid such as nitrogen, helium or argon, with a finely divided material in homogeneous and stable suspension in the liquid. The finely divided material is in the form of particles having a size between 200 and 2,000 A and is present in a quantity between 10 and 1,000 grams per liter of cryogenic liquid. The suspended material may be aluminum, titanium, zirconium, niobium, calcium, lithium, magnesium, solid glass, or an oxide of aluminum, titanium, zirconium, niobium, calcium, lithium or magnesium, and is highly reflective to infrared radiation from the metal so as to reduce the transparency of the cryogenic liquid to this infrared radiation.

What is claimed is: 
     
       1. A method of reducing heat loss from the upper surface of a body of molten metal, comprising establishing on said upper surface a layer of a cryogenic liquid selected from the group consisting of nitrogen, helium and argon, and suspending in said cryogenic liquid 10 to 1000 grams per liter of cryogenic liquid, of at least one finely divided material in the form of particles having a size between 200 and 2000 A, said material being selected from the group consisting of aluminum, titanium, zirconium, niobium, calcium, lithium, magnesium, solid glass, and an oxide of aluminum, titanium, zirconium, niobium, calcium, lithium or magnesium, thereby to maintain a homogeneous and stable suspension of said material in said cryogenic liquid and to reflect infra-red radiation from said suspended particles back toward said molten metal.